Process of purifying metals.



UNITED STATES PATENT OFFICE.

PAUL LOUIS TOUSSAINT HEROULT, OF LA PRAZ, FRANCE, ASSIGNOR TO soorErE FRANCE.

ELECTltO-METALLURGIQUE FRANCAISE, OF FROGES, ISERE,

PROCESS OF-PUR'IF YING METALS.

Specification of Letters Patent.

Patented April 23, 1907.

Application filed April 28, 1906. Serial No. 314,256.

To all whom it may concern:

Be it known that I, PAUL LOUIS TOUS- SAINT HEROULT, a citizen of the Republic of France, residing at La Praz, Savoie, France, have invented a certain new and useful Improved Process of Purifying Metals, of which the following is a specification.

The invention aims to provide an improved process for separating out the impurities of a metal, and especially for separating out impurities such as phosphorus and sulphur from steel or other varieties of iron, so as to make a steel of high purity.

Certain other features of improvement are referred to hereinafter.

A bath of the metal is prepared, and is oxidized to such an extent as to transfer the impurities therefrom to the slag whilemaintaining its melting point below the temperature of the furnace, so that it remains liquid until the transfer of the impurities is substantially complete. The metal is then solidified, while the slag is maintained molten, and the slag with the impurities is removed, after which the metal is remelted and treated as desired to obtain the final composition.

We .will describe in detail the application of the process to the purification of steel. It is assumed that a basic Siemens furnace of the tilting type is used, as this is the most convenient, but it will be apparent that the process is not restricted to any particular apparatus. The fusing point of steel or iron varies with the composition, increasing with the purity of the metal. Crucible steel (containing say 1 per cent. of carbon), forexample, fuses at approximately 1400 degrees centigrade. As the carbon is reduced,we have soft steel of say 0.10 per cent. carbon, which grade.

fuses at approximately 1600 degrees centifuses at approximately 1900 degrees cent-igrade. If, however, the iron of substantial purity (containing say 001 per cent. carbon, 0.01 per cent. phosphorus, and 0.015 per cent. sulphur) be superoxidized, its fusing point is reduced. When it contains roughly about 0.75 per cent. oxygen, its fusing point is lower than that of soft steel, both of these being well within the temperature attainable in a Siemens furnace. The present invention utilizes these variations in the fusing point, and it is assumed that the temperature of the Substantially pure iron (deoxidized)' furnace throughout the process is maintained above the fusing point of soft steel and below that of pure iron deoxidized.

It has heretofore been customary in the conversion of pigiron or scrap iron into steel, to arrest the oxidizing process at such a oint as to leave within the bath a substantia per centage of phosphorus and sulphur. The continuation of the oxidation which would be necessary to substantially eliminate the impurities, has been carefully avoided, because the iron begins to be superoxidized before the complete elimination of the impurities, and such superoxidized iron has been considered practically useless and unmanageable.

According to the present invention the oxi-, dation of the bath is continued not only until the desired percentage of the carbon has been oxidized, but beyond this point until substantially pure iron. superoxidized is obtained. In this superoxidation substantially the whole of the impurities are transferred to the slag. The ure metal is then deoxidized, so that its me ting point is quickly raised above the temperature "of the furnace. It solidifies as soon as it is sufiiciently deoxidized, and we thus have in the furnace a solid base of deoxidized pure iron very smooth on its upper surface, and upon which there is a molten slag which can be readily removed, carrying wlth it the impurities which have been extracted from the iron. It is for the purpose of dumping the slag that a tilting furnace is advantageous. The surface of the iron is so smooth that the slag may be re moved almost to the last drop. The impurities being withdrawn, the pure iron may be converted into steel of any desired composition. For example, to make soft steel or crucible steel, both of which fuse at the temperature of the furnace, it is only necessary to add carburizing materials, such, for example, as carburite (a mixture of carbon and iron) or pig iron of hi h purity. A neutral slag is also applied to t e surface of the metal to protect it from the oxidizing action of the flame. The continuance of the process will be in accordance with the usual practice, and

depend upon the product' desired, which a Any neutral s ag may be used for thelast stage of the process, "such, for example, as

lime, sand, and clay, or other materials which will be fluid and protect the metal from the flame. The slag is not expected to exert any chemical effect on the steel, inasmuch as there is nothing to be removed therefrom.

After the final melting of the steel, it may receive the usual additions of manganese, silicon, aluminum, or the like, to ensure the casting of sound ingots as far as possible. I By this process steel of very high purity may be obtained from very poor or impure stock.

The heat of the furnace referred to herein is the heat to which the metal in the furnace as not to deoxi ize the bath, until and with is brought.

The process may also be carried out in an electric furnace without substantial variation of the details described;

Though I have described with great particularity of detail a specific process embodyin my invention, yet it is not to be understoo that the invention is limited to the particular process described.

Various modifications thereof in detail may be made by those skilled in the art without departure from the invention.

What I claim is r 1.. The process of making iron or steel of high purity, which consists n formin a bath of steel and superoxidizing it by adfition of ore and by exposureto oxidizing flame and thus transferring the impurities to the slag, feeding scrap or ig iron to the bath so slowly substantially the desired total charge is reached, adding pig iron at such a rate as to raise the meltlng point above the heat of the furnace to solidify the metal, removing the slag the impurities from the solid metal sosigned my name in that only the substantially pure solid metal remains, and adding a carburizing material of high purity and introducing a neutral slag to protect the surface of themetal from the oxidizing influence of the flame, until the meltin oint is loweredto a point below the heat of tlie furnace. 2. The process of making high purity, which consists 1n of steel and superoxidizing it impurities to the slag, materials to raise the melting point above the heat of the furnace and to solidify the metal, removing the from the solid metal, and addin a neutral sla and carbon to lower the me ting point an form a molten bath of iron substantially free from impurities.

3. The rocess of separating impurities from a bati'i of steel, which consists in oxidizing it sufficiently to transfer the impurities to the sla while maintaining its melting point below t e temperature of the furnace, solidifying the steel while maintaining the slag molten, and removing the slag with the im purities.

4. The rocess of separating impurities from a bath of steel, which consists in oxidizing it suflicie'n'tly the sla below t forming a bath to transfer the to transfer the impurities to While maintaining its melting oint e temperature of the furnace, eo'xidizing the steel to raise its melting point above the temperature of the furnace and to solidify it while maintaining the slag molten, and removing'the slag with the impurities.

5. The process of separatin the slag completely from a bath of steel, w 'ch consists in solidifying the steel While maintaining the slag molten, and removing the molten slag from the solid steel.

In witness whereof, I have hereunto thepresence of two subscribing w'itnesses.

.PAUL LOUIS VTOUSSAINT HEROUL'I.

iron or steel of adding deoxidizing' slag with the impurities 

